1. Field of the Invention
The present invention relates to: a viewing-angle control device to control a viewing angle of a display device; a display apparatus; a method for controlling a viewing-angle control device; a viewing-angle control program; and a storage medium storing the program.
2. Description of the Related Art
Conventionally, liquid crystal displays (LCD) have been widely employed as display devices of portable electronics devices such as portable phones and PDAs (Personal Digital Assistant). Having narrow viewing angles, LCDs have been considered to be disadvantageous compared with CRTs (Cathode Ray Tube) and plasma displays, but recent advancement in LCD technologies has allowed widening of the viewing angles.
However, there is a possibility that, when the portable electronics devices are used in crowded situations in trains, buses, and the like, people around the portable electronics devices peek at what is displayed on a display screen of the portable electronics devices. Especially in creating or reading an electronic mail, it is undesirable in view of privacy that details of the electronic mail are peeked by people around the portable electronics devices.
In response to this problem, there has been suggested an LCD that allows controlling a viewing angle (see Patent Documents 1 to 4, for example). Generally, such LCDs are switchable, from one to the other, between a normal wide viewing-angle mode and a narrow viewing-angle mode, in which the viewing angle is narrow. The narrow viewing-angle mode is a mode in which a displayed image is visible in a normal way from the direct front of the display screen where the user is, and a plain image or a different image is visible from a sideward direction.
For example, in the viewing-angle variable device of Patent Document 1 (Japanese Unexamined Patent Publication No. 105958/1997 (Tokukaihei 9-105958) (publication date: Apr. 22, 1997)), a liquid crystal layer between a pair of substrates becomes a narrow viewing-angle when liquid crystal molecules are aligned vertically to the substrates, while the layer becomes a wide viewing-angle when the molecules are aligned parallel to the substrates. Further, in the portable terminal device of Patent Document 2 (Japanese Unexamined Patent Publication No. 62094/2004 (publication date: Feb. 26, 2004)), the viewing angle of the information displaying means is changed by changing an alignment of liquid crystal between two glass plates.
Further, there has also been a display apparatus divided into several sections, each of which is differentiated from one another in alignment direction and the like, whereby, during the narrow viewing-angle mode, an image different from what is displayed on a display screen is visible when the display screen is seen from a direction other than the front. For example, Patent Document 3 (Japanese Unexamined Patent Publication No. 264768/2001 (publication date: Sep. 26, 2001)) teaches a liquid crystal display apparatus in which alignment layers sandwiching a liquid crystal layer are divided into a plurality of areas, each of which is differentiated in alignment direction from its adjacent areas. Further, Patent Document 4 (Japanese Unexamined Patent Publication No. 38035/2004 (publication date: Feb. 5, 2004)) teaches a liquid crystal display apparatus in which a first liquid crystal cell and a second liquid crystal cell are alternately disposed, and the first liquid crystal cell and the second liquid crystal cell are different in viewing-angle direction from each other.
Furthermore, in the portable terminal device of Patent Document 2, the viewing angle is controlled on the basis of a type of an application being executed. This makes it possible to change the viewing angle automatically on the basis of a situation of use, allowing the user to avoid bothersome operation to determine the viewing angle every time.
In recent years, as CPU has improved in processing capacity and has increased in storage capacity, the number of application to be installed has increased not only in ordinary electronics devices but also in portable electronic devices. Therefore, it is a burden to manufacturers and users to set a viewing angle for every application to be used.